Despite recent progress, the first stages of cloud fragmentation and core collapse remain poorly known. Significant observational advances were achieved in this field over the last decade, thanks to the use of large (sub)millimeter radiotelescopes such as the IRAM 30 m and the JCMT. Young protostars ("Class 0" objects), featuring powerful jets and marked infall motions, were identified at the beginning of the main accretion phase. The density structure of numerous prestellar condensations was also measured, setting strong constraints on the initial conditions for individual collapse in molecular clouds. More recently, the advent of large-format bolometer arrays has allowed complete imaging of several nearby protoclusters in the submillimeter. The results suggest that stars are generally built from finite reservoirs of mass and imply that the stellar initial mass function (IMF) is at least partly determined by turbulent fragmentation at the prestellar stage of star formation. This field will greatly benefit from future large submillimeter projects such as FIRST/Herschel and ALMA in which Europe is involved at the highest level.